Emotionally detaching

I’m at my ends rope with my bf. It’s been a long hard 3 years. I’ve probably only been happy with him 35% of the time.. which is sad. We have a daughter together that’s a few months old & we live together. I’m trying to learn to how emotionally detach from him while we live in the same home! Any advice on that? We barely have sex anymore, we don’t sleep in the same bed. We did a few days ago & that was for a night. I just can’t get other the thought of him messing with someone else and i wanna get to the point where i just don’t care.. how can i do that? How can i make it so that thought doesn’t bother me? What are other things i can do to emotionally detach?